Generally known for its reproductive role, the hormone prolactin is now known to be released in response to stress. Acute psychological stress reliably increases prolactin and affects behaviors in adult male rats; however, responses of adult females and juvenile males and females remain to be explored. In the proposed experiments, four psychological stressors will be examined: novel open field, noise, the conditioned-emotional- response (CER) paradigm, and nonpainful exposure to a cat. As a second component, the present slate of experiments will examine the impact of a conspecific on responses to psychological stressors by testing animals in the presence of a same-sex littermate. A third component, pre-treatment with 1 mg/kg i.p. injection of the oxytocin antagonist 1-deamino-2-D-Try-(Oet)-4-Thr-8-Om-oxytocith will examine the possible role of oxytocin in social buffering as measured by prolactin levels. Prolactin and individual as well as social behaviors in the stressful environments will be recorded. It is hypothesized that adult male and female rats tested alone in the chamber will have lower levels of prolactin than those tested alone in the chamber with a stressor. Low levels of prolactin are also expected in females exposed to a stressor in the presence of a conspecific, and the oxytocin antagonist is expected to block oxytocin in the pre-treated conspecific females, resulting in high levels of prolactin comparable to those found in animals tested alone with a stressor. Conversely, adult males may not experience social buffering and are expected to have high levels of prolactin in the social condition; therefore, pre-treatment with an oxytocin antagonist will not cause higher levels of prolactin as compared with the non-treated social animal. Among juvenile males and females, no such sex X treatment condition interaction is expected. Juveniles are expected to respond to stress, social buffering, and the oxytocin antagonist in a pattern similar to adult females (above). Each animal model will serve as a foundation to build an understanding of responses to stress and social buffering, particularly in nonverbal populations such as children, the aged, and adults with brain injuries.